IJR International Journal of RailwayVol. 6, No. 3 / September 2013, pp. 90-94

Vol. 6, No. 3 / September 2013 90

The Korean Society for Railway

An Environmentally Friendly Soil Improvement Technologywith Microorganism

Daehyeon Kim* and Kyungho Park†

Abstract

Cement or lime is generally used to improve the strength of soil. However, bacteria were utilized to produce cementa-tion of loose soils in this study. The microo rganism called Bacillus, and CaCl2 was introduced into loose sand and softsilt and CaCO3 in the voids of soil particles were produced, leading to cementation of soil particles. In this study, loosesand and soft silt typically encountered in Korea were bio-treated with 3 types of bacteria concentration. The cementa-tion (or calcite precipitation) in the soil particles induced by the high concentration bacteria treatment was investigated at7 days after curing. Based on the results of Scanning Electron Microscope (SEM) tests and EDX analyses, high concen-tration bacteria treatment for loose sand was observed to produce noticeable amount of CaCO3, implying a significantcementation of soil particles. It was observed that higher calcium carbonate depositions were observed in poorly gradeddistribution as compared to well graded distribution. In addition, effectiveness of biogrouting has also been found to befeasible by bio-treatment without any cementing agent.

Keywords : Bacteria, Soil, Biotreatment, Cementation, Biogrouting, Cementing agent

1. Introduction

Bio-treated soil improvement technology has recentlybeen suggested (Mitchell and Santamarina 2005) andattempted by several researchers (Dejong et al. 2006,Whiffin et al. 2007, Paassen et al. 2010, Kim et al. 2012,Park and Kim 2012; 2013).

Although a number of bacteria can be found in the soil,Bacillus pasteurii has been commonly used in producingmicrobial cementation of soil particles. This is becauseBacillus pasteurii uses urea as an energy source and pro-duces ammonia, which increases pH in the neighboringenvironment, causing Ca2+ and CO3

2- to precipitate asCaCO3(Stocks-Fisher 1999, Bachmeier et al. 2002,Dejong et al. 2010).

The principle of microbially induced cementation of soil

is as follows:As shown in equation 1), bacteria eats urea and CO3

2-

and 2NH4+ are produced through hydrolysis. Then, cal-

cium carbonate (calcite) is precipitated(see equation 2).

CO(NH2)2 + 2H2O CO3

2- + 2NH4+ (1)

CO32- + Ca2+

→ CaCO3 (2)

†

*

Corresponding author: Department of Civil Engineering, Chosun University, KoreaE-mail : munhakng@nate.comDepartment of Civil Engineering, Chosun University, Korea

ⓒThe Korean Society for Railway 2013http://dx.doi.org/10.7782/IJR.2013.6.3.090

Fig. 1 Cementation of soil particles through calcite precipitation

91

Daehyeon Kim and Kyungho Park / IJR, 6(3), 90-94, 2013

Fig. 1 shows a schematic of how calcite precipitation(CaCO3) fills the voids of soft soil and creates cementa-tion of soil particles.

2. Findigs of Cementation Using Microorganism

2.1 Cementation of soils

Figs. 2 and 3 compare the difference in the cementationfor two sand specimens(which has been presented at Kimet al.(2011): one for No- Bacteria-Treatment and anotherfor High-Concentration-Bacteria-Treatment.

The specimens were oven-dried for 24 hours at a tem-perature of 110o

in Celsius, seven days after curing. Asshown in Figs. 2 and 3, no indication of cementationbetween particles is observed in the No-Treatment sand,while a clear cementation between particles is observed inthe High-Concentration-Bacteria-Treatment sand.

2.2 Effect of ground conditions

The mixing ratio of silty sand specimen used in thisstudy was 1:1 for the microbial solution and the calciumchloride solution as shown in Table 3. Relative density

was set to 60%, 75% and 90% for different ground condi-tions to conduct the laboratory test so as to identify thelevel of created calcium carbonates depending on the levelof compaction.

SEM produces 2-dimensional data which is similar to 3-dimensional images and allows depositions created on thesurface of soil particles to be accurately observed. Theresult of SEM analysis by the magnification of 5000 timesfor the tested specimen is shown in Fig. 4. It was identi-fied that the portion with the highest Ca number was circu-lar, and calcium carbonate depositions by microbes were

Fig. 2 No treatment sand(at 7 days after curing)

Fig. 3 High concentration bacteria treatment(at 7 days after curing)

Table 1. Specimen Mixing Ratio Depending on theLevel of Compaction

SpecimenRelative

Compaction (%)

Soil(g)

Calcium Chloride

Solution (ml)

Microbial Solution

(ml)

SM

60 223 10 10

75 279.3 11.5 11.5

90 297.4 13 13

Fig. 4 SEM results for (a) Dr 40%, (b) Dr 60%, (c) Dr 80%, (d) Relative compaction 60%, (e) Relative compaction 75%, (f) Relative compaction 90%, (g) Well graded, (h) Poorly graded

An Environmentally Friendly Soil Improvement Technology with Microorganism

92

observed. The portions used in analyzing the result inEDX analysis is represented as a square to reveal the Cacontent in the relevant portion.

EDX belongs to the electronic microscope family and isanalysis equipment in which a scanning electron micro-scope is combined with an energy dispersive x-ray spec-trometer, and used to analyze which elements are includedin a small amount of sample. Therefore, it was intended toidentify the level of calcium carbonate depositions withthe Ca element content to be identified.

In the comparison of Ca content, the relative density of60% exhibited the highest calcium carbonate deposition.This illustrates that, if voids are too loose, soil particles arenot reasonably combined, to result in the low level of cal-cium carbonate depositions.

The highest calcium carbonate deposition was exhibitedat 90% of relative compaction, which is the first reactionsoils other than sand, and it was identified that highercompaction levels contributed to higher calcium carbon-ate depositions. However, the difference is insignificant.Other soils than sand should be further studied.

With respect to well graded distribution and poorlygraded distribution, EDX analysis revealed lots of cal-cium carbonate depositions in poorly graded distribution.The result was that, because uniform voids were created inpoorly graded soil, it was accordingly identified thathigher calcium carbonate depositions were observed inpoorly graded distribution as compared to well graded dis-tribution.

2.3 Applicability of biogrouting

Soil cementation by microbes is achieved by: creatingcarbon dioxide (CO2) and ammonium (NH4) through ure-ase (enzyme for hydrolysis of urea) in the microbial solu-tion which is a new environment-friendly material toproduce carbonates (HCO3); and mixing calcium chloridesolution (CaCl2) which is a reactive solution to enable thecalcium carbonate (CaCO3) to deposit in the voids of soilto firmly cement soil particles. An exemplary method ofcementing the soft ground is the injection technique.Instead of using cement or liquid, the environment-friendly grout material of microbes is used to inject themicrobial solution and the reactive solution to integratemicrobes with grouting technique to produce a bio-groutmaterial which is an environment-friendly material.

Studies on bio-grouting are still at the experimentalstage. The microbes for bio-grouting are used in variousfields in addition to the geotechnical engineering. For bio-grouting, the grouting technique used in geotechnical engi-neering is integrated with bio-grout materials to enablemicrobes to permeate into voids between particles and

then to fill the voids between grounds with calcium car-bonate depositions more closely. This method achieves theeffect of increasing strength and preventing the flow ofwater. In this study, we identified the effect of preventingthe flow of water in the soft ground with bio-grout mate-rial through the permeability test. The added reactive solu-tion was calcium chloride of 0.75Mol for microbialdeposition. The microbes (KCTC 3558) B. pasteuriipassed through voids between the soil particles wheninjected, but they are enlarged to be 0.06 mm - 0.1 mm insize, approximately 20 times larger if mixed with the reac-tive solution and calcium carbonate deposition occurs. Forthis reason, it is necessary to have enough voids to allowmicrobes to freely move when the microbes grow throughthe microbial reaction.

2.3.1 Effect of biogrouting on hydraulic conductivity A closed cylinder model device (5 cm12 cm) was pro-

duced, other than the injection hole and the drainage wayon top and on the bottom for smooth injection and drain-age. A porous plate was installed on the bottom of thedevice to avoid the solution in which the microbes areinjected and water to flow out. The specimen was put andthe porous plate was installed to avoid flowing onlythrough a given part. As shown in the following Figure, awater head difference was made. Fig. 5 shows the cylindri-cal model device and the process of injecting the micro-bial solution.

In the permeability test, the non-treated sand specimenexhibited very high permeability of approximately 2.2710-2

(cm/s). The normal-concentration treated specimen exhib-ited the permeability of approximately 6.3010-3(cm/s),approximately 30% higher than the non-treated specimen.This implies that was achieved by the fine calcium carbon-ate particles deposited in voids between particles.

Fig. 5 Permeability test with cylindrical model device(5 cm 12 cm)

93

Daehyeon Kim and Kyungho Park / IJR, 6(3), 90-94, 2013

It was identified that the non-treated sandy silt speci-men exhibited a low permeability of approximately 4.5210-4(cm/s) as shown in Table 2. In the case of normaltreatment, the permeability was approximately 1.5710-4

(cm/s), approximately 35% higher than non-treated speci-men, which is a high effect of reducing the permeability. Itwas identified that reducing the permeability was made bythe fine calcium carbonate particles deposited in voidsbetween particles.

2.3.2 Effect of biogrouting on the strength of soil Table 3 shows the mixing ratio of specimens for differ-

ent types of injection methods such as injection withsyringe (drained and undrained), injection with air-com-pressor. In the injection with syringe, the same amount ofbacteria and Calcium chloride were used. A total of250 ml was injected for five days (25 ml/each injectionand twice a day), while in the injection with air-compres-sor, a total of 250 ml was injected one time at a pressure of0.5 kPa.

Fig. 6(a) and 6(b) shows the process of air-compressor

injection. Fig. 7 shows the results of the cementation for each

injection method. The thicknesses of cementation withundrained test, drained test and air-compressor injectiontest are 3.5 cm, 4.5 and 5.4 cm, respectively. The compres-sive strengths of undrained test, drained test, air-compres-sor injection test are 80 kPa, 100 kPa and 150 kPa,respectively. The reason why the air-compressor injectionyields the largest cementation thickness and the highestcompressive strength is that the injection pressure wasdone at a constant rate and infiltration of the solution wasin a stable manner, resulting in enhanced cementation inthe air-compressor injection.

Table 2 Results of permeability test for sand

Specimen TreatmentVolume of

Passage (cm3)

Water Head

Difference (cm)

Time(sec)

Permeability (cm/s)

Sand

Non-treatment

780 59 300 2.2910-2

783 59 300 2.3010-2

775 59 300 2.2810-2

Normal-concentration

treatment

215 59 300 6.5010-3

210 59 300 6.3510-3

200 59 300 6.0510-3

Table 3 Mixing ratio of test specimen

Specimen ConditionSoil(g)

CaCl2

(ml)

Normal concentr

ation bacteria

(ml)

Water(ml)

D60×H120(mm)

Non treated Soil 375.9 - - 500

Normal concentr

ationbacteria

Undrained test

375.9 250 250 -

Drained test

375.9 250 250 -

Air compressi

on injection

test

375.9 250 250 -

Fig. 6 (a) Air compressor injection,(b) Process of Biogrouting test

Fig. 7 Test result (a) Undrained test, (b) Drained test,(c) Air compressor injection test

Fig. 8 Compressive strength with different mix

An Environmentally Friendly Soil Improvement Technology with Microorganism

94

In order to evaluate the effectiveness of the treatmentwith microorganism, different treatment methods wereattempted. Fig. 8 compares the unconfined compressivestrength for different treatment methods such as non-treated soil, cement 4%, cement 2%+CaCO3 2%, cement2% and CaCO3 2%. Note that the unconfined compres-sive strength was measured 3 days after mixing. As shownfrom Fig. 8, the unconfined compressive strengths of non-treated soil, cement 4%, cement 2%, cement 2%+CaCO3

2%, cement 2% and CaCO3 2% are 175 kPa, 195 kPa,220 kPa, 255 kPa and 230 kPa, respectively. Based on thetest results, it is noted that the strength of cement2%+CaCO3 2% is higher than that of cement 2%. Thisimplies that bio-treatment with microorganism is found tobe feasible in the soil improvement, leading to reduction inthe use of cement.

4. Conclusions

Based on the results of the study, the following conclu-sions can be drawn.

1. A clear cementation between particles is observed inthe High-Concentration-Bacteria-Treatment sand.

2. Based on the SEM analyses and EDX analyses, thefeasibility of cementation for loose sand with bacteriatreatment is confirmed both quantitatively and qualita-tively.

3. The normal-concentration treated specimen exhibiteda permeability of 6.3010-3(cm/s), which is approxi-mately 30% of reduction in permeability. This proves thatthe microbial cementation is effective in reducing the flowof water in the soil.

4. Based on the test results, it is noted that the strengthof cement 2%+CaCO3 2% is higher than that of cement2%. This implies that bio-treatment with microorganism isfound to be feasible in the soil improvement, leading toreduction in the use of cement.

Acknowledgments

This research was supported by Basic Science ResearchProgram through the National Research Foundation ofKorea(NRF) funded by the Ministry of Science, ICT andFuture Planning(NRF-2013R1A1A1AO5010106).

References

1. Bachmeier, K. L., Williams, A. E., Warmington, J. R., Bang,S. S. (2002). “Urease Activity in Microbiologically-inducedCalcite Precipitation,” Journal of Biotechnology, Vol. 93, pp.171-181.

2. Deong, J. T., Fritzges, M. B., Nüsslein, K. (2006). “Microbi-ally Induced Cementation to Control Sand Response to Und-rained Shear,” Journal of Geotechnical and GeoenvironmentalEngineering, Vol. 132, pp. 1381-1392.

3. Dejong, J. T., Mortensen, B. M., Martinez, B. C., Nelson, D.C. (2010). “Bio-mediated Soil Improvement,” Journal ofEcological Engineering, Vol. 36, pp. 197-210.

4. Kim, D. H., Kim, H. C., Park, K. H. (2011). “Cementation ofSoft Ground Using Bacteria,” Korea Patent 10-1030761,pp.1-47.

5. Kim, D. H., Kim, H. C., Park, K. H., Lee, Y. H. (2012).“Effect of Microbial Treatment Methods on Biogrout,” Jour-nal of Korean Geo-Environmental Society, Vol. 13, pp. 51-57.

6. Kim, D. H., Park, K. H., Kim, S. W., Mun, S. H. (2012). “ANovel Approach to Induce Cementation of Loose Soils,”Advanced Science Letters, Vol. 9, pp. 545-550.

7. Kim, D. H., Park, K. H. (2013). “Injection Effect of Bio-grout for Soft Ground,” Advanced Science Letters, Vol. 19,pp. 468-472.

8. Mitchell, J. K., Santamarina, J. C. (2005). “Biological Con-siderations in Geotechnical Engineering,” Journal of Geo-technical and Geoenvironmental Engineering, Vol. 131, pp.1222-1233.

9. Paassen, L. A., Ghose, R., Linden, T. J. M., Star, W. R. L.,Loosdrecht, M. C. M. (2010). “Quantifying BiomediatedGround Improvement by Ureolysis,” Journal of Geotechni-cal and Geoenvironmental Engineering, Vol. 136, pp. 1721-1728.

10. Park, K. H., Kim, D. H. (2012). “Verification of CalciumCarbonate by Cementation of Silt and Sand using Bacteria,”Jounal of Korean Geotechnical Society, Vol. 28, pp. 53-61.

11. Park, K. H., Kim, D. H. (2013). “Strength and Effectivenessof Grouting of Sand Treated with Bacteria,” Jounal ofKorean Geotechnical Society, Vol. 29, pp. 65-73.

12. Stocks-Fisher, S., Galinat, J. K., Bang, S. S. (1999). “Micro-biological Precipitation of CaCO3,” Soil Biology and Bio-chemistry, Vol. 31, pp. 1563-1571.

13. Whiffin, V. S., Paassen, L. A., Harkes, M. P. (2007). “Micro-bial Carbonate Precipitation as a Soil Improvement Tech-nique,” Geomicrobiology Journal, Vol. 24, pp. 1-7.